1. Technical Field
The present invention relates to an electrostatic induction generator.
2. Background Art
Conventionally there is well known an electrostatic induction generator, in which a pair of substrates that can move relatively while remaining opposed to each other is provided, plural electrets are arrayed in one of the substrates, and plural sets of pairs of electrodes are arrayed on the other substrate. In the electrostatic induction generator, an electrostatic capacitance between one of the pair of electrodes and the electret and an electrostatic capacitance between the other electrode and the electret change by the relative movement of the pair of substrates respectively, whereby the change amount is output as an electric power.
Assuming that the pair of electrodes is made of the same material and has the same configuration and that the pair of substrates moves relatively (moves reciprocally) so as to oscillate at a constant frequency f, Boland, et al. say that a maximum output power Pmax is expressed by Pmax=σ2nA2πf÷[(ε e ε 0/d)×((ε e g/d)+1)]. Hereinafter, the above mathematical formula is referred to as an equation 1.
At this point, σ is surface charge density in the pair of electrodes, n is (amplitude of the pair of substrates÷a pitch between the electrets), A is a maximum area in which the electret and the electrode overlap each other, εe is specific permittivity of the electret, d is a thickness of the electret, ε0 is vacuum permittivity, and g is a gap between the pair of substrates.
According to the equation 1, it is necessary to increase n in order to enhance the output power. That is, it is necessary to increase the amplitude of the pair of substrates or to decrease the pitch between the electrets. However, when miniaturization of the electrostatic induction generator is demanded, there is a limitation to the increase in amplitude of the pair of substrates. In such cases, the output power can be increased on the equation 1 by decreasing the pitch between the electrets.
However, actually it is demonstrated that the output power cannot be increased as calculated even if the pitch between the electrets is decreased. According to a report, this is attributed to the fact that a parasitic capacitance generated in one of regions of the electrostatic induction generator degrades power generation efficiency (see Non-Patent Document 1). However, it has been unclear which region, in which the parasitic capacitance is generated, degrades the power generation efficiency.
Related technologies are disclosed in Patent Documents 1 to 3.
Patent Document 1: Japanese Unexamined Patent Publication No. 2008-161036
Patent Document 2: Japanese Unexamined Patent Publication No. 2009-77614
Patent Document 3: Japanese Unexamined Patent Publication No. 2008-252847